To reduce wind flow resistance and drag on a semi-trailer truck, trailer, a pup trailer, tractor, semitrailer, or other vehicle, aerodynamic devices may be used to redirect and control the flow of air passing around the vehicle. During operation of a tractor-trailer truck, air around the tractor-trailer truck may flow between the tractor unit and the trailer, or underneath the trailer, and impart a drag force to the trailer. Aerodynamic devices are designed to control the air flowing into the gap formed between the tractor unit and the trailer and underneath the tractor and trailer. Such reduction on the drag of the vehicle may conserve fossil fuels, as well as other sources of vehicle drive power for hybrid vehicles, battery-operated vehicles, and alternative fuel-based vehicles, for example.